#!/usr/bin/perl
use Tk;
use warnings;
use strict;

my $mw = MainWindow->new(title => "Timer");
my $elapsed_sec = 0;
my $elapsed_sec_label = $mw->Label(-textvariable => \$elapsed_sec)->pack();

my $repeater; # declare first so it can be accessed in the callback
    
$mw->Button(-text => "reset", 
     -command => sub {
               $elapsed_sec = 0;
               &repeater();
             })->pack();

$mw->Button(-text => "exit", 
     -command => sub { exit })->pack();

# start first run
&repeater();
               
MainLoop;


sub repeater{

#this is repeated every second, and you can put your is_playing here
$repeater = $mw->repeat(1000 => sub {

               $elapsed_sec ++;
               
               if ($elapsed_sec > 4){ $repeater->cancel }
               
               }  ); 
      
}